Alkaline storage cells with cadmium type negative electrodes



ALK LINE STORAGE CELLS WITH CADMIUM TYPE NEGATIVE ELECTRODES No Drawing.Application July 11, 1957 Serial No. 671,146

. 7 Claims. (Cl. 1361-24) N. J., assignor to Elgin, 111., a corporationof This invention relates to alkaline storage cells of the type whichuse a cadmium active material in the negative electrodes, and moreparticularly it relates to an improved cadmium-active material for suchcells having a novel addition agent or expander.

The phrase cadmium active material is herein used to refer topulverulent materials composed predominantly of cadmium hydroxide oroxide with or without varying minor proportions of iron active material,and the phrase iron active materia is used to refer to pulverulentmaterials composed of substantially equal amounts of finely-dividedmetallic iron and ferrous oxide. When such cadmium active material iselectrolytically reducedi. e., charged or formedit becomes principallyfinelydivided metallic cadmium with or without a small percentage offinely-divided metallic iron depending upon whether iron active materialwas initially included. It is intended that the phrase cadmium activematerial as herein employed comprehends both its reduced and unreducedstates. Further, although negative electrodes of the cadmium type aretypically employed with positive electrodes having an active materialcomposed principally of nickel oxide, no unnecessary limitation of theinvention in connection with such positive electrodes is intended.

An object of the invention is to provide an improved cadmium activematerial for alkaline storage cells which is adapted to provide thecells with improved operating characteristics, greater capacity andlonger life.

Another object is to provide alkaline storage cells having an improvednegative active material of the cadmium type which is adapted tomaintain the life of the cells after many cycles of charging anddischarging.

A further object of the invention is to provide an improved activematerial of the cadmium type having therein a new addition agent orexpander which is easy and economical to use.

These and other objects and features of my invention will be apparentfrom the following description:

It is well known in the art of making battery electrodes that certainaddition agents or expanders, depending on the type of battery employed,are elfective in retarding a densifying of the active material and ingiving the batteries therefore better operating characteristics, greatercapacity and longer life. The present invention is in the discovery thatpolyvinylpyrrolidone is a very effective and economical addition agentor expander for the cadmium active material of negative electrodes ofalkaline storage cells.

My invention may be carried out using the usual cadmium active materialcomposed of ten parts of cadmium hydroxide or cadmium oxide prepared asby anodic electrolysis of cadmium material in an aqueous alkalineelectrolyte, plus about one part of active iron material. The averagecadmium content of such hydroxide or oxide is of the order of 75% andthe iron content of such iron active material is of the order of 89%.With this cadmium active material there is intimately mixedapproximately.l% by weight of polyvinylpyrrolidone on a cadmium metalbasis. This new addition agent may be provided in dry form, in whichcase it is added to the dry cadmium active material and thoroughlymechanically mixed therewith. When added in powder form, about 375% g.of the addition agent is used for each 50 g. of cadmium active material.Alternatively, the polyvinylpyrrolidone may be added in liquid form, inwhich case about .375 g. of the addition agent is dissolved in 10 ml. ofwater and this solution is added to about 50 g. of cadmium activematerial. After this solution is thoroughly mixed with the cadmiumactive material the mix is dried at about 100 C. over.- night and thenstrained through a 20-mesh screen. The end product is packed under heavypressure into the pockets of the usual pocketed 'form of negativeelectrodewith each pocket containing typically about 8 g. of th cadmiumactive material. Since the-mechanical form of such electrodes is wellknown and the invention is not involved in the mechanical nature of theelectrode, the same is not herein shown or described.

In a different verision of the invention the polyvinylpyrrolidoneaddition agent or expander may be added to plain cadmium active materialhaving no iron active material content. Although the addition of a minorproportion of iron active material to cadmium hydroxide or oxide is wellknown as providing an improved form of cadmium active material fornegative electrodes, the use of a small percentage, of the order of 1%by weight of the cadmium metal, of the present new addition agent toplain cadmium active material is found to have even a greater benefit. I

Each storage cell used for testing the present invention may compriseone single-pocket negative electrode and two nickel oxide positiveelectrodes having excess electrical capacity. Such cell may be tested byrepeated charge and discharge cycling wherein each cycle consists ofcharging the cell for about 15 hours at 500 ma. and then discharging thecell at a current of 400 ma. to a terminal voltage of 1 volt. Forcomparison purposes, similar cells without the present new additionagent have also been cycled in the same way.

It has been found that with addition of the polyvinylpyrrolidone thereis a small loss of the order of about 5% in the initial capacity butthat this loss occurs only during the first 8 to 20 cycles. Thereafter,those cells with the addition of the polyvinylpyrrolidone outperform theregular cells of similar construction and size. For example, it is foundthat as the cycling is continued the relative performance of those withthe new addition agent becomes increasingly better, the capacity of thenew cells after about 300 cycles being approximately 60% to better.Still further, it is found that the new addition agent is substantiallymore effective in connection with plain cadmium active material than itis with the more usual cadmium active material including a minorproportion of iron active material. In this connection the capacity ofthe storage cells with the plain cadmium active material plus the newaddition agent is, after about 300 cycles, of the order of 5% to 10%higher than it is with similar cells differing only in that the cadmiumactive material includes also about 10% by weight of iron activematerial.

Although the new addition agent of my invention is preferably added tothe cadmium active material directly as above described, the inventioncomprehends the addition of this new agent in other ways as, forexample, by adding it directly to the electrolyte.

The description of my invention is intended to be illustrative thereofand not lirnitative thereof since the Pat Jan- 20, 19.52

3 invention is subject to changes and modifications without departurefrom the scope thereof, which I endeavor to express according to thefollowing claims.

Iclaim: l r I l. A negativeelectrode for alkaline'storage cellscomprising an intimate mixture of cadmium active material and ofpolyvinylpyrrolidone as an addition agent in an amount effective toincrease substantially the life of the electrode.

2. The negative electrode set forth in claim 1 wherein said cadmiumactive material is composed predominantly of cadmium hydroxide with aminor proportion of iron active material.

' 3. The negative electrode set forth in claim 1 wherein theamount ofsaid addition agent is about 1% by weight of the cadmium metal.

4. A dry, pulverulent active material for the negative electrodes ofalkaline storage cells consisting essentially of a predominantproportion of a material selected from the group consisting of cadmiumhydroxide and cadmium oxide, plus about one percent by weight of thecadmium metal of polyvinylpyrrolidone as an addition agent.

5. A dry, pulverulent active material for the negative electrodes ofalkaline storage cells consisting essentially of an intimate mixture ofa material selected from the group consisting of cadmium hydroxide andcadmium oxide, plus about ten percent of iron active material and aboutone percent of polyvinylpyrrolidone as an addition agent.

6. An alkaline storage cell comprising a positive electrode having anactive material of nickel oxide, a negative electrode provided with acadmium active material, an alkaline electrolyte, and an addition agentof polyvinylpyrrolidone in the cadmium active material in an amountefiective to increase substantially the life of the negative electrode.

7. An active material for negative electrodes of alkaline storage cellsconsisting essentially of an intimate mixture of cadmium active materialand of a small percentage of polyvinylpyrrolidone as an expander.

References Cited in the file of this patent UNITED STATES PATENTS2,519,399 Roberts Aug. 22, 1950

1. A NEGATIVE ELECTRODE FOR ALKALINE STORAGE CELLS COM PRISING ANINTIMATE MIXTURE OF CADMIUM ACTIVE MATERIAL AND OF POLYVINYLPYRROLIDONEAS AN ADDITION AGENT IN AN AMOUNT EFFECTIVE TO INCREASE SUBSTANTIALLYTHE LIFE OF THE ELECTRODE.